Interpretive Summary: Peanut production and seed quality are severely constrained by a wide variety of diseases. The most promising solution for managing peanut diseases is using resistant cultivars. A high yielding cultivar with disease resistance would present tremendous advantages for peanut farmers to fight the diseases. The objective of this study was to identify expressed resistance gene analogs (RGAs) from peanut expressed sequence tags (ESTs) for marker development. By using known R gene protein sequences to screen peanut ESTs, 385 unigenes were identified as peanut expressed RGAs. A total of 28 simple sequence repeats (SSRs) were identified from 25 expressed RGAs. One SSR marker of RGA121 and two PCR-based markers, Ahsw-1 and Ahsw-2, from RGA013 were polymorphic in two mapping populations. All three markers were mapped on the same linkage group AhIV, which will be useful in future isolation of resistance genes and genetic study in peanut.

Technical Abstract: Cultivated peanut is an important source of protein and oil. However, low genetic diversity makes peanut vulnerable to many diseases. Several hundred of partial genomic DNA sequences targeting nucleotide-binding-site leucine-rich repeat (NBS-LRR) resistance (R) genes have been reported. Only a small portion of these have transcripts. Therefore, the objectives of this study were to identify expressed RGAs from peanut expressed sequence tags (ESTs) and to develop markers in mapping populations. By using 54 known R gene protein sequences to screen peanut ESTs, 1,053 ESTs identified were targeting different classes of known R genes. After assembly, 385 unigenes including 156 contigs and 229 singletons were identified and considered as peanut expressed RGAs. There are 69, 191, 82, 28, 11, and 4 expressed RGAs for NBS-LRR, protein kinase (PK), LRR-PK/transmembrane (TM), Toxin reductase, LRR, and TM domain encoding R genes, respectively. A total of 28 simple sequence repeats (SSRs) were identified from 25 expressed RGAs. One SSR marker of RGA121 and two PCR-based markers, Ahsw-1 and Ahsw-2, from RGA013 were polymorphic in mapping populations. All three markers were mapped on the same linkage group AhIV, which will be useful in future isolation of resistance genes and QTL study in peanut.